There is known a laser telemeter which includes a laser generator suitable for sending a light pulse towards a target, a photoelectric receiver disposed to receive an echo of this pulse returned by the target and means for measuring the interval of time between the emission of the pulse sent by the generator and the return of the echo at the receiver. Receivers of telemeters of this type are generally semi-conductor components of small dimensions, e.g. avalanche diodes which can detect very low-power light pulses; but these components can be blinded temporarily or put out of action if they receive light engergy which is too powerful.
When such telemeters are installed on military equipment, it may happen that two telemeters fitted on equipment of opposing armies aim at each other. Then, if a laser pulse emitted by one of the telemeters enters the receiver system of the other, the receiver of the latter may in some conditions be damaged either temporarily or permanently. Further, a telemeter of one of the two armies may be subjected to systematic firing of countermeasure light pulses coming from telemeters or illuminators which belong to the enemy army. Finally, it appears that during a military operation between equipment equipped with telemeters of this type, there is an appreciable probability that some telemeters will thus be prematurely put out of action.
The present invention aims to mitigate this disadvantage and to produce a laser telemeter which is capable of withstanding systematic or accidental firing of counter-measure pulses.